This species may be common in deep waters of the Great Barrier Reef, however its density fluctuates more than 100% annually due to seasonal changes. This species is generally absent during the cooler months (April through October). Although this species population trend has not been extensively monitored, it is thought to be stable.

In December 1989, a density of 284 shoots/m² was recorded at Fitzroy Island, of which only 5-10% were male (Kuo et al. 1993).

This species is present in the subtidal zone, generally deeper than four m. This species is seasonal and is fast growing, forming dense beds. This species may actually be spreading with trawling within some parts of its range. It has been found in shallow coastal habitats (near mangrove and estuaries) and deep waters of the Great Barrier Reef lagoon. It is found in areas with predominantly fine mud with some carbonate sand and shell grit. It occurs in small patches of monospecific meadows but is more commonly mixed with H. decipens and sometimes other species. This species is an annual that germinates, grows, flowers, and fruits within a few months. Fruits are borne on erect shoots and float, which results in wide dispersal (Kuo et al. 1993).

Halophila tricostata has high seed production, with rates of 70,000 seeds/m²/year in the Great Barrier Reef region. This is an annual species in eastern Australia, only appearing in late September through to February and being sustained by a sizeable seed bank. It is ephemeral with rapid turn-over and high seed set, and is well adapted to high levels of disturbance.

This species was originally described from Lizard Island where it was collected offshore between 15-30 m. It was growing sparsely amongst dense mixed stands of H. spinulosa (dominant), H. ovalis, and H. decipiens on a surface substrate of coarse coral sand, shell fragments and foraminiferans. It is found in Queensland on the tropical coastline and Great Barrier Reef Complex, Lizard Island, and Magnetic Island (Greenway 1979).

This species is threatened by sediment loads in water, coastal development, dredging and marine developments, and minor damage from boating and shipping activities. It also could be impacted by coastal runoff and to some extent trawling activities (Green and Short 2003).

This species is present in remote locations, and has not been extensively monitored. Therefore, more research is needed on its biology and population status.

Most of this species' range lies within the Great Barrier Reef National Marine Park and World Heritage Sites and associated State Marine Parks.The Queensland Fisheries Act allows destruction only when a permit has been assessed and issued. It is protected in either Fisheries Act or in National Park or Marine Park Acts in New South Wales and Queensland (Green and Short 2003).